Messages Are Disappearing

(Read the last paragraph if you don’t care for backstory)

So I was talking with an acquaintance and realised they were talking about doing an immoral action to this girl which I cannot discuss about. Basically I wanted to tell the girl but when I went to look at the messages to show as proof, they were cut out for some reason. It didn’t seem like it was ban worthy but it was just cut out from the rest of the conversation. Every part of the conversation was there except for that one part.

Is there an explanation or fix to specific messages being erased from a conversation in a chat?